It is known in the art to use support columns, particularly those that permit limited height adjustability of the column, for supporting elements of a structure, such as upper floors. As described in U.S. Pat. No. 5,056,750 to Ellithorpe, early columns used a structural column having a single, threaded support rod extending therefrom (Canadian patent 136,200 to Beichert and Canadian patent 704,587 to Russo). Further, support assemblies are known having central threaded members to which flanking members are attached for forming a saddle for engaging elements such as structural beams (Canadian patent 949,056 to Ratliff). Similarly, supports are known which provide upwardly and inwardly inclined jack units having levers and braces, such as chains, between angled bases and opposite converging tops of screw jacks, such that when the braces are tightened, the heads function as jaws (Canadian patent 642,534 to Teel). Additionally, columnar structures are known in which adjustment of column height requires adjustment not only of the thickness of baseplates, but also of nuts and bolts throughout the column (Canadian patents 675,000 to Dielman and 968,118 to Antoniou).
As well, a complex combination of a jack screw, levelling nut, tension plate and U-shaped bolt, arranged transversely rather than longitudinally with respect to a beam and passing through the tension plate to be fastened on the lower side thereof by hold down nuts, is known from Canadian patent 970,353 to McMichael.
Some of the above-mentioned patents describe devices suitable for permanent support, whilst others are more suitable for temporary support. In addition, the above-mentioned prior art patents present devices that are somewhat complex, both in their structure and in their manner of use and have poor moment carrying capacity.
In Applicant's U.S. Pat. No. 5,056,750, now expired, a moment-resisting member is placed centrally between height adjustment means. Moment-carrying capacity is provided by a saddle comprising a load engaging member having threaded rods flanking a telescopic assembly, substantially reducing a prior “hinge connection” at the top of columns. As well, the telescopic assembly absorbs bending loads whereas the flanking threaded rods carry compressive loads only. The resulting saddle is also adjustable in height even when loaded.
As will be understood by those of skill in the art, wind causing upward lifting of a structure and excessive lateral loading, can cause structural damage and potential collapse, as can seismic activity. Excessive lateral loading can cause a structural frame to deflect from a normal square or rectangular shape to form a parallelogram. The shift to the parallelogram compromises the structural integrity of the frame and may ultimately lead to partial or complete collapse of the structure.
Further uplift, generally as a result of wind lifting, may cause damage to the roof, weakening the structural integrity. As wind flows over the building, the pressure directly above the surface of the roof decreases. At the same time, internal air pressure increases due to air infiltration through openings, cracks, etc. The result is a net upward force on the roofing system.
It is currently known to minimize uplift and the effects of lateral and shear loading, such as during an earthquake or high-wind situation, including but not limited to a tornado. Applicant currently provides a series of pre-engineered steel columns, marketed as WM series columns, which can be used with or without known means for preventing uplift. In the case where uplift is addressed, beams supported by the structural columns are fastened thereto, such as by bolting to a top plate supported on the column or to a saddle attached to the top plate. Further, a base of the column is secured to a base structure, such as a footing, such as by bolting the base plate thereto. The column is then secured to the base plate, such as by welding or by passing a bolt through both the square column and an upstanding member welded to the base plate. In some cases, concrete is poured over the footing and around the base of the column for additional support.
Generally, pre-engineered steel support columns are designed to support vertical or compression loading only. Recent changes to building codes, such as to part 9 of the National Building Code (NBC) require measures to prevent uplift of the structure, over and above those currently incorporated in existing support columns and as described above for the WM series columns. Specifically the changes to the NBC are included in new section 9.23.13, titled “Bracing to Resist Lateral Loads due to Wind and Earthquake.
Thus, there is a requirement and therefore great interest in the industry to ensure that columns, particularly when used as part of a braced wall panel or shear wall, are capable of meeting building code requirements for lateral loading and lifting, such as from wind and seismic activity.